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New study says Pfizer vaccine effectiveness drops to 47% by the sixth month

A biochemistry professor at Georgia Tech said the decrease in efficacy is no surprise. Here's why.

ATLANTA — Ashley Nealy has been part of a Pfizer vaccine study since August of 2020 and got her first dose more than a year ago. So, a newly published study showing Pfizer efficacy against infections drops from 88% in the first month to 47% by the sixth month was not news she wanted to hear.

"I definitely was concerned," she said. "I always knew there was the possibility we'd need to get boosters but I didn't think it would happen after 6 months.

"It definitely gave me pause but I was still thinking some protection is better than none at all," said Nealy.

Dr. M.G. Finn, a biochemistry professor at Georgia Tech, said the decrease in efficacy is no surprise.

"The overall protection the vaccine affords degrades over time, lessens over time," said Finn.

Finn said that holds true for all three vaccines, but there’s important context to consider in Pfizer’s case. Finn said because Pfizer came out first, a larger portion of the elderly and those who are immunocompromised have gotten this particular vaccine.

The efficacy data may be influenced by this vulnerable population to a certain degree. Finn said that doesn't mean another vaccine is better.

"You did not make a mistake by getting any of the three vaccines that were approved," said Finn.

Finn said the older a person is, the more quickly the vaccine will diminish; the same is true for people who have certain health conditions that put them more at risk – like obesity.

And while only Pfizer is approved to offer boosters, that could change as more data comes in on the other vaccines.

"Right now [it is] for populations at risk, and later perhaps for the general population," said Finn.

As Nealy, she said she is getting her booster shot next week. The Pfizer study runs for a full two years, so she will remain in that study until August of 2022.